Module 4 : Electrical Switches and Their Types

Single Pole Double Throw (SPDT) Switch

Three way switch.

Double Pole Single Throw (DPST) Switch

Safety switch, panelboard breaker (switch).

Double Pole Double Throw (DPDT) Switch

Transfer switch.

Electric Switch

A device intended for on-off control of circuits and electrical isolation of equipment; a piece of apparatus or device for making, breaking, or changing the connection in an electrical current in the circuit.

Pole

That part of a switch, which is used for making or breaking connection, and which is electrically insulated from other contact.

Throw

The direction from a given position in which the contact is made, also indicates the number of times a contact is made.

Single Pole Single Throw (SPST) Switch

Single pole switch.

Single Throw Switch

Will make a closed circuit only when a circuit is thrown in one position.

Double Throw Switch

Makes a closed circuit in either one of the two positions.

Voltage Rating

Switches are rated in the following manner: 120V, 220V, 600V - normal building equipment, 5KV, 15KV - special switches and switchgear.

Number of Poles

1, 2, 3, 4, etc.

Number of Closed Positions

Single throw, double throw, etc.

Isolating Switch

A switch intended for isolating an electric circuit from the source of power. It has no interrupting rating and is intended to be operated only after the circuit has been opened by some other means.

Motor Circuit Switch

A switch, rated in horsepower, capable of interrupting the maximum operating current of the motor of the same horsepower rating as the switch of the rated voltage.

Transfer Switch

A device for transferring one or more load conductor connections from one power source to another.

Control Function

Single acting, Three way, Four way, etc.

Duty

General use or safety switches intended for general light and power circuits may be Heavy Duty (HD), Normal Duty (ND), or Light Duty (LD), Load-interrupting duty.

Method of Operation

Manual, magnetic, motor operated, etc.

Method of Protection

Non-fused, fused, circuit breaker, combination, etc.

Enclosure

Open, enclosed, weathertight, watertight, explosion-proof, etc., all switches except snap switches or knife switches mounted on a switchboard must be enclosed in an appropriate cabinet as a means of protection from external damage.

Fusibility

A switch may be constructed with or without provision for a fusing.

Methods of Engaging Contact

Sliding, snap, liquid (mercury), etc.

Number of Breaks

Single break, double break, etc.

NEC Rating

General service, isolating, motor duty, etc.

Other Functions

Dimming or voltage control, photoelectric, time clock, electrically or mechanically held, auxiliary controlled such as pressure, thermal, flow, infrared, motion, proximity sensitive, etc.

General Use Switch

A switch intended for general use in general distribution and branch circuits. It is rated in amperes, and it is capable of interrupting its rated current at its rated voltage.

Single Pole Switch

A switch that opens and closes only one side of a circuit.

General Snap Switch

A form of general switch so constructed that it can be installed in flush device boxes or on outlet box covers, or otherwise used.

Double Pole Switch

A term designating two contacts or connections on a device, for instance, a double knife switch.

Three-way Switch

A switch used when it is desired to control lights from two different locations; the light may be turned on or off from either points.

Flush-type

Consists of a switch mechanism mounted in a porcelain or composition-moulded case with the complete unit to be mounted inside a switch box, outlet box so that the operating handle or button is the only portion of the switch which extends beyond the cover of the switch box.

Four-way Switch

Used in conjunction with two three-way switches, wherein it is desired to control lights from three or more locations.

Pendant Switch

Used for control of lamps or other devices which are mounted overhead.

Canopy Switch

A small, compact switch for mounting in canopies of lighting fixtures for the control of lamps directly at the fixture.

Multi-circuit Switch

Used for the control of lights in a multi-lamp fixture.

Switch Operation

Switches may be operated by electromagnets, motors, or solenoids, and referred to as manual or electromagnetic-operated switches.

Lever Switch

Most power switches are operated by means of simple lever action, or by means of a lever attached to the switch through a mechanical device.

Momentary Contact Switch

Used when it is desired to open or close a circuit for a short length of time. The switch is provided with a spring so that it will return to its original position as soon as the handle or button is released.

Surface Switch

A switch that is mounted on the surface of a wall.

Drum Switch

The blades of a button switch are operated by a rocking action through a spring-and-cam mechanism.

Tumbler Switch (Toggle Switch)

This is operated in a manner similar to the push-button switch, except that the blades are activated by a lever instead of a button.

Switch Combinations

Consists of a set of contact segments mounted on a movable drum and a set of stationary contact fingers. These are used for motor starting control and instrument switches.

Dial Switch

A switch that can control multiple locations with specific combinations of switches.

Single-Pole Switch

Consists of a movable contact mounted on an arm that can be rotated and with several contacts arranged in circular form.

Snap Switch

A small capacity switch in which the circuit is made broken with a quick motion independent of the speed of the operation of the operator.

Rotary Switch

The switches move in rotary motion by means of a handle through a spring-and-cam mechanism.

Push-Button Switch

A switch that is activated by pressing a button.